This invention relates to a novel process for producing a heterocyclic compound having a nitromethylene group as the side chain group.
Heterocyclic compounds having a nitromethylene group as the side chain group find uses in agricultural chemicals, pharmaceuticals or perfumes. For example, Japanese Unexamined Patent Publicaion No. 151882/1975 proposes tetrahydro-2-(nitromethylene)-1,3-thiazines having excellent activities as agricultural chemicals such as pesticides and acaricides.
In the prior art, most of the processes for preparation of heterocyclic compounds having a nitromethylene group as the side chain employ as the starting material cyclic dithiocarbamic acid esters which can easily be synthesized and are also highly reactive.
For example, the above Unexamined Patent Publilcation discloses the following process as the process for preparation of tetrahydro-2-(nitromethylene)-1,3-thiazines.
First, tetrahydro-1,3-thiazine-2-thion is methylated with a methyl halide, the resultant tetrahydro-2-(methylthio)-1,3-thiazine is allowed to react with an alkyl nitroacetate in the presence of zinc ions to give an alkyl nitro(tetrahydro-1,3-thiazine-2-ylidene)acetate, which is then hydrolyzed in the presence of a base, followed by decarboxylation to prepare a desired product of tetrahydro-2-(nitromethylene)-1,3-thiazine.
As can be seen from this example, the process for preparation of a heterocyclic compound having a nitromethylene group as the side chain group, using a cyclic dithiocarbamic acid ester as the starting material involves reaction steps which are very lengthy and complicated, and methyl mercaptan which may cause offensive odor is generated in the step of reacting the methylated starting material with an alkyl nitroacetate. Thus, this process cannot necessarily be stated to be satisfactory in industrial application.